add example to calculate psidiag(Rdiag,Zdiag) at specific diagnostic...

add example to calculate psidiag(Rdiag,Zdiag) at specific diagnostic Rdiag,Zdiag values from equilibrium psi(R,Z), as well as rhopol, rhotor etc. This is used in gdat,AUG now

git-svn-id: https://spcsvn.epfl.ch/repos/TCV/gdat/trunk@4424 d63d8f72-b253-0410-a779-e742ad2e26cf